The invention relates to devices and related systems and methods for affecting transmission of a first light beam passing through a layer from one side through use of a second light beam incident on the layer from the other side. The invention finds application in fields such as optical signal processing, optical computing, optical sensing and optical spectroscopy.
The common wisdom in optics is that light beams travelling in different and even opposite directions pass though one another without mutual disturbance. This is known as the superposition principle of linear optics.
In order to allow light signals to interact in such a way that one light signal can modulate or control another light signal, a non-linear medium is used in which intense optical fields provided by lasers interact. Such arrangements allow the superposition principle to be broken in nonlinear optics.
However, using non-linear effects in a non-linear medium for beam interaction typically requires intense laser fields thereby necessitating high power consumption and significant costs. These features of non-linear interactions make light-by-light modulation either unavailable or unsuitable for many applications, such as data processing, where it could otherwise be very useful.
Composite and layered structures have attracted recent interest to provide so-called coherent perfect absorption (CPA), i.e. to absorb the entirety of an incident laser beam.
Dutta-Gupta et al, “Controllable coherent perfect absorption in a composite film” Optics Express, vol. 20 p. 1330-1336 (2012) describe how a metal/dielectric composite might be used to achieve coherent perfect absorption (CPA) in a plasmonic metal/dielectric composite slab of thickness d=5 μm which is illuminated by coherent light from both sides of wavelength λ=562 nm. The light wavelength is matched to the plasmon resonance of the slab which is at around λ=540 nm. The paper suggests tuning the plasmon resonance of the composite by varying the volume fraction of the metal.
Pu et al, “Ultrathin broadband nearly perfect absorber with symmetrical coherent illumination” Optics Express, vol. 20 p. 2246-2254 (2012) describe how a thin layer of tungsten of thickness 17 nm can be used as a CPA device. A tungsten CPA is expected on the basis of the metal's bulk dielectric permittivity to have an operational wavelength range of 800 nm-1500 nm and also have absorption over a very broad wavelength range, so it is suggested for use in a solar cell for absorbing sunlight.